Major technological benefits have been enabled by the ability to explore and engineer systems with controlled mechanical properties across multiple length scales. A prime example is the Eiffel tower in Paris consisting of mechanical elements at three distinct length scales thus achieving an unprecedented degree of stability. This concept of hierarchical mechanical properties has been transferred to research new microstructures with enhanced physical properties such as polymer gels, foams and biological materials such as bones, cells and tissues.
However engineering systems in the micron to mm scale is extremely challenging due to the lack of techniques to accurately measure the mechanical properties locally within the material, at the abovementioned scales. Currently it requires a combination of conventional techniques such as bulk rheology (mm scale) with e.g. atomic force microscopy (micron scale). This has severe drawbacks as (a) not all intermediate length scales can be probed and (b) only some techniques are compatible with living materials such as cells and tissues. In particular there is no technique to probe the mechanics of living tissues and/or cells as these develop in embryos, adult organisms and disease processes, spatially in the micron to mm range. Also, it would be very useful to be able to measure the spatiotemporal mechanical properties of soft materials (whether inert or living), as these measurements would allow the connection of the local mechanical properties and structure at the microscale with the mesoscopic and macroscopic mechanics of the system. The mechanical (material) properties of the cellular microenvironment are physical quantities that control cell behavior. The compliance or fluidity to which cells are exposed acts as a signal that can affect critical cells behaviors, for example, cell differentiation and regulation of tumor progression. Currently, there is no available technique to quantify the local mechanical properties of the cellular microenvironment. The mechanical behavior of cellular aggregates has been studied in vitro by micropipette aspiration and microindentation techniques. Unfortunately, these techniques cannot be used in vivo, inside developing embryos and in disease processes in living organisms. Laser ablation has been used to estimate the mechanical properties of living tissues, but cannot provide a quantitative measure because the forces driving tissue relaxation are unknown. Only optical tweezers have been recently used at sub cellular scales to measure the mechanical properties of the cell cortex. None of the mentioned techniques allows the precise application of controlled forces at the necessary spatial and temporal scales to quantify cellular and tissue mechanics during embryonic development, adult organs and/or disease processes (such as tumor progression).